It is critically essential that petroleum wells have suitable provision for protecting the well against certain hazards commonly encountered in the operation of such wells. Abnormal conditions can be encountered suddenly and without advance notice. Thus there may be a sudden release of undergrounding pressure causing the well to go wild and out of control. Even under normal operating conditions it is often desirable to interrupt flow at sub-surface depths.
To meet the foregoing and the like contingencies numerous cut-off valve constructions have been proposed heretofore incorporating the capability of responding to emergency conditions to interrupt flow. Although these various types are in widespread daily use, they are subject to certain disadvantages and shortcomings avoided by this invention. One common type employs a flapper valve pivotally supported along the interior sidewall of the flow passage and held open by a protector tube so long as normal operating conditions prevail. Some safety valves of this type respond to an abnormal increase in the flow velocity to close automatically whereas others are held in open position hydraulically by static pressure means controlled from the ground surface. Another type of safety cut-off valve in use employs a rotary ball valve held in open position by hydraulic pressure controlled at the well head. Among the serious shortcomings of certain of these valves is the fact that one or more springs is relied upon to close the valve operating mechanism and these springs are required to operate in opposition to the static hydraulic head in the line employed to open the valve. For this reason, it has been found impractical to utilize such valves at a depth in excess of about 500 feet. This is a highly objectionable and serious limitation on land based wells, and particularly as respects wells beneath the sea bed. Moreover, prior safety cutoff valves lack the capability of control at will from ground level as well as the ability to close automatically in response to abnormal rapid flow.
To avoid the foregoing and other limitations and shortcomings of prior safety cut-off valve constructions, there is provided by U.S. Pat. No. 4,002,202 issued to Huebsch and Paulos an improved safety cut-off valve having an electromagnetic operating mechanism controllable from the surface by power leads extending along the tubing annulus. The operating mechanism functions equally well to open either a flapper or ball-type valve. The cut-off valve assembly functions in a highly satisfactory manner at any desired depth, the valve-opening operation being facilitated at greater depths by first equalizing the pressure on the opposite sides of the valve from ground in accordance with techniques well known to those skilled in this art. The valve assembly, with the exception of the solenoid coil subassembly, is installable and retrievable by wire line operating techniques or alternatively by retrieving all or part of the tubing string. The solenoid coil must be energized to open the flow control member and to hold it open. If power fails for any reason or is deliberately cut off, spring means, acting alone or in cooperation with flow past the valve quickly closes the valve and positively prevents further flow. Additionally, both species of this improved safety cut-off valve close automatically if flow increases abnormally for any reason.
However, our aforedescribed safety valve is subject to certain limitations. For example, many wells are so constructed that there is not unlimited space between the tubing string and the well casing. This is especially true as respects certain tubing retrievable valves in which the tubing string bore through the valve mechanism is the same as that of the tubing string and this unadvoidably increases the outside valve diameter over that of wire line type valves. Due to valve construction and operating characteristics there are numerous limitations confronting the designer difficult to resolve when using solenoids to operate the valve.